Magnetographic printing machines are known which make it possible, in response to the reception of electrical signals from a control unit, to form images, such as images of characters, on a printing carrier, typically a tape or a sheet of paper. In these printing machines, which are similar to those described and shown in U.S. Pat. No. 3,161,544, printing of the images is done, first, on the basis of the signals received, by forming a latent magnetic image on the surface of a magnetic recording element, typically in the form of a rotating drum or endless belt, this recording element being coated with a film of magnetic material. The latent magnetic image is then developed, or in other words made visible, with the aid of a powdered developer. Because it comprises fine particles of thermoplastic resin including magnetic particles and pigments, the developer is attracted only by the regions of the recording element on which the latent image has been recorded; the developer then forms an image in powder on the surface of the element. Subsequently this image in powder is transferred to the printing carrier.
To permit forming the latent magnetic image on the surface of the recording element, these machines are provided with a recording device known as a transducer, which includes one or more magnetic recording heads, in proximity with which the recording element is displaced. Each of these heads, whenever it is excited for a brief moment by an electrical current of suitable intensity, generates a magnetic field, the effect of which is to create magnetized domains of small dimensions on the surface of the recoring element moving past them; these virtually point-shaped domains are typically known as magnetized points.
The set of these magnetized points comprises the latent magnetic image. The portion of the surface of the recording element that thus passes before each head is typically known as the information recording track, and in general the recording element includes a plurality of tracks that can be subjected to recording, either individually in the course of successive recording operations, or simultaneously in the course of a single operation.
In magnetographic printing machines, each of the printed characters is the product of the printing on the printing carrier of a set of points located inside a matrix; each of these points is obtained by the transfer of particles of developer previously deposited onto a corresponding magnetized point of the recording element onto the carrier. Since the magnetized points that are formed on the recording element are always of very small dimensions, for instance on the order of 66 .mu.m, and the distance (from center to center) that separates two continguous points is slightly greater than the size of these points, for instance on the order of 100 microns, it has been confirmed that when using these points to produce standard characters, having a height equal to one-tenth of an inch (that is, approximately 2.54 mm), it was quite difficult to form certain characters having curved or oblique lines in their configuration, such as the characters "V", "W", "X", "Y", "M", "C", "3", and "7".
In fact, considering the relatively wide spacing between two adjacent points located on an oblique line, the curved or oblique portions of these characters always appear broken up and not as dark. Naturally, to obtain lines that are thicker and hence are more visible it is known that these lines can be reinforced by using more than one contiguous lines of points to form each of these lines, instead of only one line of points. For example, to make the oblique line of the character "N", two or three contiguous oblique lines of points can be used. However, this procedure proves to be not entirely satisfactory, because the characters having curved or oblique lines that are obtained thereby, although quite legible, still look more or less deformed.
To overcome this disadvantage, the attempt has been made to utilize a solution described in French Patent No. 2.042.947, which comprises reducing the spacing between the lines of points, without also modifying the size of the points or the dimensions of the characters. However, although this solution made it possible to improve the aesthetic qualities of the characters, it proved to be totally unadapted to the case of magnetographic printers, because it necessarily meant that the magnetized points that are formed on the recording element had to be overlapped, which reduced the force of magnetic attraction in the central portion of each of the zones formed by the overlap of these points considerably, and thus led to insufficient inking of the characters.
Naturally this defect can be eliminated by reducing the size of the points, taking into account the reduction in spacing between the lines of points, so as to eliminate the overlapping effect, but that procedure necessitates further increasing the number of lines of points constituting each of the lines of the characters, and so necessitates a major increase in the number of circuits serving to form the points, as well as in the equipment assuring the electrical supply to the circuits; the resultant printing machine is particularly bulky and expensive. Moreover, this kind of procesure does not enable satisfactory correction of the deformation of the characters.